It is sometimes desirable to allow telephone subscribers to transmit signaling information, such as dialed digits, over a previously established communication path through the telephone switching network. For example, when a subscriber with a remote terminal wishes to communicate with a computer via a telephone switching system, it is common for the subscriber to dial information to the computer after the telephone system has completed a communication path between the subscriber's remote terminal and the computer. Many telephone system communication paths, however, include DC blocking at some point therein. If the subscriber has a subscriber set which transmits alternating current (AC) signals to represent dialed digits, he can communicate through a switching system on a communication path of the above type since the AC signals are transmitted through the DC block. Dial pulses, however, are changes in the DC conductivity of the subscriber loop which are blocked by the DC blocking present in telephone communication paths. Accordingly, signaling through the telephone switching network may be denied to rotary dial subscribers who can transmit only dial pulses. It is possible to include an arrangement in a telephone central office which detects dial pulses on the communication path and which transmits on that path coded AC signals representative of the dial pulse sequences. In this manner, subscriber signaling information can be transmitted through or around the DC block contained by the communication path.
Many present day telephone switching systems, however, continually scan the conduction state of communication paths to detect flashes or on-hook indications from subscriber sets. These indications from the subscriber are used by the telephone switching system to control the establishment and maintenance of the communication path. It is possible that sequences of dial pulses will be erroneously detected by a telephone switching system as flash or on-hook indications. The telephone switching system may then disconnect the subscriber or provide the service associated with a flash, e.g., conference or third party calling, when such is not desired.
An arrangement in accordance with the present invention allows rotary dial subscribers to transmit signaling information on a switching system communication path while inhibiting erroneous detection by the switching system of subscriber flash or on-hook signaling.